Our studies are directed toward learning how the biosynthesis of the uterine luteolysin, PGF2 alpha, is regulated during the ovine estrous cycle. Our working model is that levels of PGH2 synthase, the first enzyme in the prostaglandin biosynthetic pathway, are elevated in uterus by estradiol following an initial period of progesterone priming. We are testing this hypothesis by measuring levels of uterine PGH2 synthase (a) in estradiol treated, progesterone-primed animals and (b) in animals whose ovaries have been cauterized/X-irradiated to eliminate follicular estradiol secretion. We are also attempting to isolate enriched populations of uterine cells to determine the cellular site of changes in PGH2 synthase.